The invention relates generally to water pumps and more particularly to water pumps powered by solar energy.
Water, not oil, is the most precious commodity in some parts of the world today and will be in the future. Water shortages present a critical problem. Contamination of the water supply is almost as serious. To solve these problems requires adequate supplies of water of sufficient purity to drink, to use industrially, and to irrigate agricultural lands without contaminating the resulting food chain.
Unfortunately, in many developing countries, particularly in parts of Africa and Asia, where millions of people have faced and continue to face famine caused by drought conditions or severe population overcrowding, sufficient ground or clean surface water is present to alleviate the problem. However, these people lack the means to recover this water. Thus millions die while water is within reach. It would be desirable to have high efficiency, low cost water pumps available so that each village or local area, including the peri-urban "squatter" communities surrounding many cities, could become self sufficient in water. A water pump which can irrigate 5 acres of land or supply the water needs of villages or groups of up to 2500 people would be particularly useful.
A wide variety of water pumps are available, including diesel, electric, mechanical, solar-electric (photovoltaic), and hand pumps. However, none of these offer an optimal combination of low cost, low maintenance and operation, and high water volume. In many undeveloped areas electrical power lines do not exist. Windmills are expensive and limited to having relatively constant high wind. A diesel system requires a supply of fuel. The estimated cost over 20 years for a diesel pump to supply a village of 2500 people is almost $40K. A photovoltaic solar (solar-electric) system includes solar cells, an electric motor, and a rotary pump, each of which is a high cost, high maintenance item. The estimated cost over 20 years for a photovoltaic powered pump to supply a village of 2500 people is greater than $30K. The simplest type of pump is of course a hand pump. However, a hand pump is very labor intensive, diverting manpower from other productive tasks, and only provides about 5% of the required volume. Thus, all the presently available pump systems have severe deficiencies which impair their suitability for large scale deployment in poor undeveloped parts of the world where they are most urgently needed.
The ideal pumping system would cost $10K or less over 20 years, or about $1.37/day, to supply a group of 2500 people, or about $0.20/person/year. The pump should be able to provide 7,000 to 16,000 gallons daily, enough generally to irrigate 5 acres, or supply 2500 people. The pump should be low power, e.g. less than 1 HP, and high efficiency.
Sunlight is plentiful in most areas of the earth, with up to 10 useful hours of sun in the warmer latitudes. A self-contained pump which requires no power source other than the sun, and which converts the sun's heat directly to physical power (as opposed to converting light to electricity through the usual solar-photovoltaic process) is highly desirable. Unfortunately, such a pump, which is particularly suitable for remote and undeveloped areas, has not been heretofore available.
U.S. Pat. No. 4,346,694 issued Aug. 31, 1982 to Moan describes a solar collector module for heating air or other gaseous heat recovery medium. A plurality of evacuated collector elements are disposed on opposite faces of a manifold in a staggered array. A central baffle divides the baffle into two parallel passageways through which the air is supplied to and removed from the collector elements. Each collector element is an elongated double wall glass tube with one open end, having the annular space between the double walls evacuated to a high vacuum. The inner wall also includes a solar energy absorbing surface. A metal distributor tube is coaxially disposed in a spaced relation within the inner wall of the collector element. The annular space between the distributor tube and the inner wall communicates with the proximate passageway of the manifold and the interior of the distributor tube communicates with the distant passageway. Thus, in the collector tubes mounted on the inlet passageway side of the manifold, the air flow is outward from the inlet passageway through the annular space and back through the distributor tube to the outlet passageway, while in the collector tubes on the outlet Passageway side, the air flow is reversed, outward from the inlet passageway through the distributor tube and back through the annular space to the outlet passageway. Thus colder air from the inlet passageway is heated by passage through the collector tubes and the heated air flows into the outlet passageway. The heated air is used in an external heat recovery system.
U.S. Pat. No. 4,016,860 issued Apr. 12, 1977 to Moan shows an alternative tubular solar energy collector design using air media. The manifold is split into separate chambers by a dividing wall. Each solar collector tube is divided in half by a divider strip. Each half of the collector tube communicates with one of the separate manifold chambers. The heated air is carried by external ducts to pass over external heat exchanger coils.
Air operated diaphragm pumps, e.g. as described in The Chemical Engineer, Dec. 13, 1990, pp. 34-38, are low cost, low maintenance, high efficiency pumps, with long operational lifetimes. Such diaphragm pumps have desirable characteristics for use in the aforementioned environments. However, the necessary compressed air supply would not generally be available. Unfortunately the heated air from the above-described solar collectors is not at sufficient pressure to operate a diaphragm pump. In a double diaphragm pump, two pumping chambers are each divided into two parts by a flexible diaphragm. The liquid to be pumped is on one side of the diaphragm, with compressed air on the other side. Since compressed air is applied directly to the liquid column separated by high temperature resistant elastomer diaphragms, this balanced load removes mechanical stress from the diaphragms to produce long life.